1. Field of the Art
The present invention relates generally to a bush assemblage which is disposed between two members in a vibration system for resiliently connecting the two members so as to damp vibrations in the system, and more particularly to such bush assemblage, especially for the pivotal connection of a suspension member in an automotive vehicle, of generally cylindrical shape which comprises an inner sleeve, an outer sleeve, and a cylindrical resilient member interposed between the inner and outer sleeves.
2. Related Art Statement
A bush assemblage used for a pivotal connection in a vehicle suspension, for example, a bush assemblage, such as a control arm bush mounted in a connecting portion between a control arm and a member of a car body side or car chassis side, is generally constructed of a couple of concentrically placed metal sleeves, i.e., an inner metal sleeve and an outer metal sleeve, with a cylindrical resilient or elastic member of rubber material interposed therebetween. Such bush assemblages are aimed to, owing to the spring characteristics of the resilient member, absorb or damp mainly vibrations in their radial direction, i.e., perpendicular direction to the axis thereof. However, the use of a relatively hard rubber material as the resilient member in such bush assemblages causes the assemblages to demonstrate relatively hard or stiff circumferential spring characteristics, i.e. spring characteristics in their circumferential direction or the direction of twisting about their axis.
Some proposals have been made so far to mitigate that undesirable circumferential spring characteristic or twisting spring action, by means of interposing a sliding member or friction-reducing means between the inner metal sleeve and the resilient member, for example: U.S. Pat. No. 3,331,642, and Japanese Utility Model Application laid open in 1984 under Publication No. 59-153736. In such proposed bush assemblages, the friction resistance between the inner metal sleeve and the resilient member is decreased due to interposing of the sliding member, and relative rotation between the sleeve and the resilient member is made considerably smooth around the axis, irrespective of the extent of radial rigidity. It allows reduction of the rigidity around the axis, while maintaining the radial rigidity of the bush assemblage.
3. Problems Solved by the Invention
In such a bush assemblage provided with the sliding member, there still remain some problems.
Possible ingress of particles (such as dirt and sand grains) and mud water between the sliding member and the inner sleeve may cause some cracks or scratches and consequently cause rusting on the sliding surface of the sleeve which is usually made of metallic material. It in turn deteriorates the sliding action itself therebetween, thereby possibly resulting in degradation of the originally aimed reduction effect of the twisting spring action by the sliding member.